1198 Effect of summer annuals on ruminal fermentation and methane output in continuous culture

Resumen

Summer annuals (SA) provide forage during the summer “forage slump”, yet research on ruminal fermentation and CH4 output of SA is lacking. A 4-unit, dual-flow continuous culture fermentor system was used to assess nutrient digestibility, VFA production, bacterial protein synthesis, and CH4 output of SA. Treatments were randomly assigned to fermentors in a 4 × 4 Latin square design using 7 d for adaptation and 3 d for collection. Treatments were: 1) 100% orchardgrass (Dactylis glomerata) herbage (HERB), 2) 50% herbage + 50% Japanese millet (Echinochloa esculenta; MIL), 3) 50% herbage + 50% sorghum × sudangrass (Sorghum bicolor × S. bicolor var. sudanense; SSG), and 4) 50% herbage + 25% MIL + 25% SSG (MIX). Feedings (60 g DM/d) occurred 4 times throughout four, 10-d periods; fermentors were fed orchardgrass herbage at 730 and 1030 h. At 1400 and 1900 h, SA treatments received SA supplements while HERB received orchardgrass. Samples for CH4 were collected 6 times daily (725, 0900, 1000, 1355, 1530, 1630 h) during d 8, 9, and 10; samples for NH3–N, VFA, and pH were taken on d 8, 9, and 10. Samples were also analyzed for DM, OM, CP, and fiber fractions for determination of nutrient digestibility, and estimation of bacterial protein synthesis. Data were analyzed using MIXED procedure of SAS (SAS Inst. Inc., Cary, NC). Apparent DM, NDF, and ADF, and true DM digestibilities were not different (P > 0.062) among treatments. True OM and CP digestibilities, and apparent OM digestibility, were not different (P > 0.084; 76 ± 2.3, 93 ± 2.4, and 66 ± 2.6%, respectively) among treatments. Total N intake was not different (P = 0.389) among treatments (2.3 ± 0.01 g N/d), but bacterial N was greater (P = 0.013) in MIL and MIX than HERB (0.33, 0.34, and 0.25 ± 0.020 g N/d). There was no difference (P = 0.296) in total VFA concentration among treatments (57.5 ± 1.16 mmol/L). There was no difference (P > 0.178) in daily CH4 output (6.7 ± 2.14 mmol/d) or CH4 per gram OM fed (1.9 ± 0.62 mg CH4/g of OM fed). Addition of SA to an herbage-based diet provided similar nutrient digestibility, VFA production, and CH4 output as HERB, suggesting SA would produce similar animal performance to that of HERB.